In the manufacture of electrical cables and particularly the manufacture of so-called solid dielectric type cables having layers of heat-curable elastomeric material therearound wherein at least one of such layers serves as an electrical insulating layer, various apparatus and methods have been proposed heretofore for applying the elastomeric material concentrically around the central conductor and then heat curing the elastomeric material in a continuous process. For example, it is known to heat cure the interior portion of such heat-curable elastomeric material by utilizing an induction heating coil to heat the central conductor and thus effect heat curing of the interior portion of such material radially outwardly. It has also been proposed to provide heat curing of electrical insulation which is around an electrical conductor by passing the insulated conductor through a heated environment to effect heat curing from the exterior portion radially inwardly.
However, while these basic heat curing techniques are known, it is difficult to heat cure an elastomeric material provided around an electrical conductor in a precisely controlled substantially uniform manner throughout its thickness so as to not over cure by over heating the interior portion and/or the exterior portion of such elastomeric material or under cure by not heating enough.
Another difficulty in using an induction heating coil to provide induction heating of a central electrical conductor and thus heat the elastomeric material from its inner portion radially outwardly simultaneously with the external heating of such elastomeric material from its outer portion inwardly is that it is generally necessary to make the supporting structure which is required to support the heating coil and/or contain or support the external heating means of a material which is either electrically conductive or magnetic. However, in making such supporting structure of electrically conductive or magnetic materials it has been found that there is excessive heat build-up of the structure due to energy losses resulting in overheating of the structure with possible failure of its mechanical properties and an excessive loss of energy making it impractical to heat the central electrical conductor.